The harsh sun and the glare off the white gravel at Guantánamo Bay's Camp Echo make it difficult to see into the small enclosure where Bisher al-Rawi is seated at a tiny, folding table. Two marines have escorted me to his prison hut.

Bisher and his friend, my other client, Palestinian Jamil al-Banna, are among half a dozen UK residents who are not to be released with the four Britons also held in Guantánamo.

Bisher, who is 38, was born in Iraq, where his father was arrested and tortured by Saddam Hussein's regime. His family fled to Britain and were granted permanent residence. He has lived in London for 22 years.

But if he is released, the US intends to repatriate him to Iraq. The British government, which is responsible for his arrest, is unwilling to intervene on his behalf.

A small, slightly-built man, Bisher is wearing an oversized, orange jump suit that swallows his diminutive frame. A flourishing black beard extends several inches in all directions. Bisher rises with difficulty. His feet are shackled at the ankle by an 18in chain that runs through an O-ring that is set into the concrete.

His hands are manacled closely together in front of him and attached to a chain around his waist. He grasps my hand in both of his and gives it a single, short thrust up and down. He does not let go of my hand. His smile is genuine. "How pleased I am to meet you," he says. I ask the military policeman to remove the restraints. After some discussion, his hands are released but his feet must remain secured. Victories here are measured in very small increments.

I am the first, non-official civilian Bisher has been allowed to see after more than two years of imprisonment in three countries.

Following the US supreme court ruling last June, which gave prisoners the right to appeal to a federal court, I began to work with the Centre for Constitutional Rights in New York on behalf of Bisher, Jamil al-Banna, and British citizen Martin Mubanga, now about to be released.

Although Bisher has never met me, he must retain me at the conclusion of our meeting by signing a form prepared by the military. If he fails to do so, the military will refuse to recognise me as his counsel. Such are the rules of engagement.

Bisher looks at me and raises his eyebrows slightly. "Where shall I start?" he asks. "I guess you have a great deal to tell me," I respond.

Bisher throws his head back and laughs: "Very much. So very much!"

Next to us is the cell where Bisher is being held in isolation, 24 hours a day, when he is not being interrogated or talking with me. It is 6ft by 8ft. A surveillance camera in the ceiling monitors him. Thick metal mesh, approximately one inch square, encloses him. There is no window.

Bisher has been transferred to this cell from another camp where he was caged in a wire mesh enclosure that was roofed but otherwise completely exposed to the elements.

If he is not being punished for some minor transgression - and punishment occurs frequently - Bisher is allowed outside his cell three times a week for 30 minutes at a time. Then he is escorted by two guards to a roofed, fenced enclosure on a concrete slab that is, perhaps, 15ft by 15ft. He is alone in the enclosure.

Over two days, Bisher and I discuss his brief arrest and release by British officials in London. We then discuss his subsequent and fateful business trip to Africa to start a peanut oil factory with his brother and three other colleagues, including Jamil al-Banna.

We discuss their detention by Gambian authorities and his interrogation there by US agents, before he was illegally "rendered" to Bagram air base in Afghanistan, where he was imprisoned underground in total darkness for weeks.

We discuss the horrendous conditions and the brutal treatment he received there, where men were hung from the ceiling in chains and the screams of brutalised men prevented him from sleeping.

We discuss his lengthy incarceration. I remind him of the world beyond the gulag, about his family and world events, like the US's invasion of Iraq.

Only once during my two days with Bisher does he betray any sense of bitterness, and even then it is fleeting.

"Do you know what disappoints me most? I am disappointed in American justice. I expected so much more. When we arrived at Guantánamo and realised we were in US custody, I was confident my situation would be resolved.

"I assured my fellow prisoners that it was good to be out of Afghanistan and in American hands and that we would be fairly treated. After two years, I am no longer so foolish."

Perhaps some of the prisoners at Guantánamo posed real threats to the world at the time of their arrests. Bisher posed no threat then, and poses none now. The British and US governments both know this.

The procedures imposed on counsel as a condition of access prevent the disclosure of all the facts, circumstances and the reasons for Bisher's arrest. They also preclude me from discussing the British government's involvement in his arrest and unjust incarceration.

Bisher is jailed because of his association with a Muslim cleric named Abu Qatada, a man he has known for years, now detained without trial in the UK. Based on the evidence I have reviewed in the classified and unclassified record, Bisher is completely innocent.

Although the US government has denied that prisoners at Guantánamo are tortured, thousands of recently-released FBI documents have described the torture in horrifying detail.

Guantánamo's medical personnel, including psychologists, are active participants in the torture.

Bisher wrote me two letters on November 5 and 6. I was allowed to read his letters on December 17. He complains of being placed in solitary confinement without "comfort items".

Bisher is being punished for having a short list with the names of prisoners who want to be represented by counsel and have asked him to write to me on their behalf. He apologises for bothering me, conceding that he "needs a shoulder to cry on".

I write a letter to the military, complaining about his treatment. I do not expect a reply.

A government that engages in such abhorrent behaviour has lost its capacity to be moved by the entreaty of a lawyer to treat his client fairly and return his toilet paper.

In these cases, it is necessary to grow calluses on one's heart to prevent bleeding to death. The legal expertise of lawyers like me is probably less important than the willingness to trumpet wrongdoing in the hope of finding a receptive ear.

That's what I'm doing.

· George Brent Mickum IV is a senior partner in the Washington law firm Keller and Heckman, and the US counsel for UK residents Bisher al-Rawi and Jamil al-Banna, and British citizen Martin Mubanga